Loss of signal detection circuit

ABSTRACT

Aspects of the disclosure provide for a circuit. In some examples, the circuit includes a first inverter coupled between first and second nodes, a second inverter coupled between third and fourth nodes, and a first logic circuit having a first input coupled to the second node, a second input coupled to the fourth node, and an output, a first positive feedback circuit coupled between the first and third nodes and having a control input. The first positive feedback circuit comprises a first switch coupled between the first and fifth nodes and having a control input, a second switch coupled between the third and sixth nodes and having a control input, a third inverter having an input coupled to the sixth node and an output coupled to the fifth node, and a fourth inverter having an input coupled to the fifth node and an output coupled to the sixth node.

CROSS-REFERENCE TO RELATED APPLICATIONS

This continuation application claims priority to U.S. patent applicationSer. No. 16/535,557, filed Aug. 8, 2019, which application claims thebenefit of and priority to U.S. Provisional Application No. 62/716,415,filed Aug. 9, 2018, both of which are incorporated herein by referencein their entirety.

SUMMARY

Aspects of the present disclosure provide for a system. In at least someexamples, the system includes an embedded Universal Serial Bus 2 (eUSB2)device having a loss of signal detector. The loss of signal detectorincludes a first differential comparator having a first input coupled toa first node, a second input coupled to a second node, and an outputcoupled to a third node, a second differential comparator having a firstinput coupled to the second node, a second input coupled to the firstnode, and an output coupled to a fourth node. The loss of signaldetector further includes a first positive feedback circuit coupledbetween the third node and the fourth node, a first inverter coupledbetween the third node and a fifth node, a second inverter coupledbetween the fourth node and a sixth node, and a first logic circuithaving a first input coupled to the fifth node, a second input coupledto the sixth node, and an output.

Other aspects of the present disclosure provide for a circuit. In atleast one example, the circuit includes a first differential comparatorhaving a first input coupled to a first node, a second input coupled toa second node, and an output coupled to a third node. The circuitfurther includes a second differential comparator having a first inputcoupled to the second node, a second input coupled to the first node,and an output coupled to a fourth node. The circuit further includes afirst inverter coupled between the third node and a fifth node, a secondinverter coupled between the fourth node and a sixth node, and a firstlogic circuit having a first input coupled to the fifth node, a secondinput coupled to the sixth node, and an output. The circuit furtherincludes a second logic circuit having a first input coupled to thethird node, a second input coupled to the fourth node, and an output, aresistor coupled between the output of the second logic circuit and aseventh node, and a capacitor coupled between the seventh node and aground node. The circuit further includes a first positive feedbackcircuit coupled between the third node and the fourth node and having acontrol input coupled to the seventh node.

Other aspects of the present disclosure provide for a circuit. In atleast some examples, the circuit includes a first inverter coupledbetween a first node and a second node, a second inverter coupledbetween a third node and a fourth node, and a first logic circuit havinga first input coupled to the second node, a second input coupled to thefourth node, and an output. The circuit further includes a firstpositive feedback circuit coupled between the first node and the thirdnode and having a control input. The first positive feedback circuitincludes a first switch coupled between the first node and a fifth node,the first switch having a control input, a second switch coupled betweenthe third node and a sixth node, the second switch having a controlinput, a third inverter having an input coupled to the sixth node and anoutput coupled to the fifth node, and a fourth inverter having an inputcoupled to the fifth node and an output coupled to the sixth node.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows a block diagram of an illustrative system in accordancewith various examples;

FIG. 2 shows a schematic diagram of an illustrative circuit inaccordance with various examples;

FIG. 3 shows a diagram of illustrative waveforms in accordance withvarious examples; and

FIG. 4 shows a flowchart of an illustrative method in accordance withvarious examples.

DETAILED DESCRIPTION

Universal Serial Bus (USB) is a standard establishing specifications forinterconnect cabling, connectors, and communication protocols. Asreferred to herein, USB refers to any version of the USB specification,including any amendments or supplements, certified by the USBImplementers Forum (USB IF) or any suitable body who replaces and/oraids the USB IF in its role overseeing the USB specification, whethernow existing or later developed. In at least one example, USB, asreferred to herein, encompasses any one or more of the USB 1.0specification, USB 2.0 specification, USB 3.0 specification, USB 4.0specification, or any derivatives thereof, such as amended or “.x”variations of the above specifications. Also, as referred to herein,legacy USB refers to USB 2.x and/or USB 1.x. Embedded USB (eUSB), in atleast some examples, refers to eUSB2.

At its inception, USB was primarily intended for implementation inspecifying standards for connection and communication between personalcomputers and peripheral devices. However, as adoption of the USBstandard has expanded and implementation in computing devices of supportfor the USB standard has gained in popularity, efforts have been made toextend and expand the applicability of USB. For example, while initiallyestablishing specifications for communications between personalcomputers and peripheral devices, USB has expanded to communicationbetween peripheral devices, between personal computers, and other usecases. As a result of such widespread implementation and use of USB,efforts are being further made to utilize USB as a communicationprotocol among individual subsystems or circuits (e.g., such as asystem-on-a-chip (SoC)). Such implementations are sometimes referred toas eUSB2. New challenges arise in implementing eUSB2. For example, at acircuit level, computing devices often operate at voltage levels thatvary from those of conventional USB, creating an impediment betweendirect communication between eUSB2 and legacy USB systems. To mitigatethis impediment, an eUSB2 repeater operates as a bridge or non-linearre-driver between eUSB2 and legacy USB systems, or vice versa, totranslate between legacy USB signaling voltage levels that arecustomarily about 3.3 volts (V) and eUSB2 signaling voltage levels thatare circuit-level (e.g., silicon appropriate voltages) such as about 1.0V, 1.2 V, 1.4 V, or any other suitable value less than 3.3 V.

Signaling lines in USB and/or eUSB2 systems are, in at least someexamples, differential and bidirectional communication lines. For thisreason, in at least some implementations it becomes beneficial to knowwhen the signaling lines are available for transmission. For example,when a first device transmits to a second device over the signalinglines, in some examples it is advantageous for the second device to beable to determine that the first device is no longer transmitting andthe second device is now free to transmit to the first device over thesignaling lines. Data packets in communication between USB and eUSB2systems end with an end of packet (EOP) indicator. However, the EOPindicator does not necessarily indicate an end to transmission by adevice, merely the end of a particular data packet. Therefore, todetermine whether a device has ceased transmitting over the signalinglines, a differential voltage of the signaling lines is determined.

For example, after a final bit of the EOP indicator of communication ina USB or eUSB2 system is transmitted via differential signal lines, inat least some examples the eUSB2 specification requires a transmitter(or a circuit coupled to an output of the transmitter) to drive thedifferential signal lines low (e.g., couple each of the differentialinput signals to a ground potential through an about 40 ohm, or othercomparatively small value, resistor) for a maximum of 4 unit intervals(Uls), where a unit interval is the period of time for transmitting 1bit of data. In at least some examples, driving the differential signalslow is synonymous with driving the differential signal lines with alogic ‘0’ through a low resistance path. Driving each of thedifferential signal lines low, in at least some examples, is intended toclear each of the signal lines of any data or voltage remaining oneither of the differential signal lines. After the differential signallines are driven low, a weak pull-down is activated to place thedifferential signal lines in a high-impedance (e.g., high-z) state,enabling, in some examples, single-ended communication via either of thedifferential signal lines or a receiving device to then begintransmitting over the differential signal lines. The high-impedancestate is defined as, in some examples, coupling each of the differentialsignal lines to the ground potential (e.g., driving the differentialsignal lines with a logic ‘0’) through an about 7 kiloohm, or othercomparatively large value, resistor or resistance path. When thedifferential signal lines are driven low, in at least some examples, areceiving device is enabled to determine that a loss of signal (LOS) hasoccurred on the differential signal lines. This informs the receivingdevice that the transmitter has completed transmission and thedifferential signal lines are available for the receiving device tobegin transmitting over the differential signal lines. This LOS is, insome examples, determined by a LOS detector.

However, at least some LOS detectors are designed to have acomparatively slow response time (e.g., up to about 3 UI or longer) dueto signal filtering to prevent false or incorrect LOS detectiontriggering during normal bit transitions of data on the differentialsignal lines. In at least some implementations, such approaches areincompatible with requirements for fast response LOS detection with aminimum propagation delay. However, to remove the signal filteringcreates a possibility for false or incorrect LOS detection triggeringduring normal signal transitions, causing jitter on the differentialsignal lines when LOS detection is used to control enablement of anoutput driver, or causing other incorrect system functions. Furthermore,a filter for performing the signal filtering to prevent the false orincorrect LOS detection triggering during normal operation, in at leastsome examples, includes a resistor-capacitor (RC) filter or aninductor-capacitor (LC) filter, each of which is comparatively large insize as opposed to semiconductor devices (e.g., such as digital logiccircuits). Accordingly, a LOS detector for performing fast LOS detection(e.g., such as in 2 UI or less) while also mitigating opportunity forfalse LOS detection triggers is desirable for some circuitimplementations.

At least some aspects of the present disclosure provide for a circuit.The circuit, in at least some examples, is suitable for implementationas an LOS detector. While for the sake of simplicity the circuitdisclosed herein is described generally with respect to USB and/oreUSB2, the circuit has more broad applicability. For examples, in atleast some examples the circuit is suitable for any implementation ofLOS detection in which LOS on differential signal lines is indicated bythe differential signal lines being driven low. In some examples, thecircuit is an eUSB2 repeater suitable for use in interfacing betweeneUSB2 and USB interfaces. In other examples, the circuit is a USBdevice, and in yet other examples the circuit is an eUSB2 device.

The circuit, in at least some examples, provides for detection of LOS ondifferential signal lines within about 2 UI. At least someimplementations of the circuit explicitly do not include a filter in theoutput signal path of the LOS detection circuit for filtering an outputof the LOS detection circuit to prevent false LOS detection triggers(e.g., by filtering an output of the LOS detection circuit to delayoutput of the output of the LOS detection circuit for a predefinedamount of time to mitigate against false LOS detection triggers).Further, in at least some examples, implementation of the circuitexplicitly does not include a phase-locked loop or other clock forsignal timing, or retiming at the chip level. To implement the LOSdetection without filtering in an output signal path to mitigate falseLOS detection triggers, in at least some examples, the circuit includesone or more comparators for determining a magnitude of signals presenton the differential signal lines and one or more switchable positivefeedback circuits and/or components. Implementation of the positivefeedback circuits, in some examples, reduces a non-overlapping region ofoutput for outputs of the one or more comparators, thereby mitigating apossibility of the non-overlapping region of operation causing a falseLOS detection, thereby achieving a comparatively fast (e.g., about 2 UIor less) squelch detection time (e.g., determination that both lines ofthe differential signal lines have been driven low).

Turning now to FIG. 1, a block diagram of an illustrative system 100 isshown. In at least some examples, the system 100 is illustrative of acomputing device, or elements of a computing device. For example, thesystem 100 includes a processor 105, an eUSB2 device 110, an eUSB2repeater 115, and a USB device 120. In at least some examples, theprocessor 105 includes, or is coupled to, a transmitter (TX) 125 and areceiver (RX) 140, and the eUSB2 repeater 115 includes a TX 130, a RX135, and a LOS detector 150. The USB device 120 is a legacy USB device,as described elsewhere herein. In some examples, one or both of theeUSB2 device 110 or the USB device 120 is implemented external to thesystem 100 and configured to couple to the system 100 through anappropriate interface (e.g., such as a port and receptacle suitable forperforming communication according to eUSB2 or USB protocol,respectively. The processor 105 is, in some examples, a SoC. The eUSB2device 110 is any device operating in both ingress and egresscommunication directions according to signal voltage levelspecifications for eUSB2. The USB device 120 is any device operating inboth ingress and egress communication directions according to signalvoltage level specifications for legacy USB. For example, in at leastsome implementations the USB device 120 is a peripheral such as a userinput device, (e.g., a sensor, a scanner, an imaging device, amicrophone, etc.), an output device (e.g., a printer, speakers, etc.), astorage device, or any other peripheral, component, or device suitablefor communicating with the processor 105.

The eUSB2 repeater 115 communicatively couples the processor 105 to theUSB device 120 and vice versa, converting signals appropriate for theprocessor 105 to signals appropriate for the USB device 120 and viceversa. For example, in some implementations signaling in the processor105 is performed in a range of about 0.8 V to about 1.4 V. Similarly, insome implementations signaling in the USB device 120 is performed atabout 3.3 V or about 5 V. In at least some examples, the eUSB2 repeater115 operates as a bit-level repeater, receiving signals from one of theprocessor 105 or USB device 120 and converting the signals for use bythe other of the processor 105 or USB device 120 (e.g., by shifting avoltage level of the signals upward or downward based on a direction ofthe communications). For example, in at least some implementations theTX 130 transmits data to the RX 140 according to eUSB2 protocols. Insome examples, differential data communicated in the system 100 beginswith a start of packet (SOP) indicator and ends with an EOP indicator.

In at least some examples, the TX 125 transmits data according to eUSB2protocols or standards via differential signal lines 145 that isreceived by the RX 135 and the TX 130 transmits data according to eUSB2protocols or standards via the differential signal lines 145 that isreceived by the RX 140. For example, when the LOS detector 150determines that the TX 125 has stopped transmitting to the RX 135 viathe differential signal lines 145, in at least some examples, the TX 130transmits data via the differential signal lines 145 to the RX 140. Insome examples, the LOS detector 150 determines that the TX 125 hasstopped transmitting to the RX 135 via the differential signal lines 145when both polarities of the differential signal lines 145 are driven low(e.g., such that values present on both polarities of the differentialsignal lines 145 are less than a predefined threshold for indicatingthat the differential signal lines 145 are idle). The LOS detector 150determines that the differential signal lines 145 have been driven low,in some examples, by determining a magnitude of both positive andnegative polarities of the differential signal lines 145. Thedetermination is made, in some examples, by one or more comparators (notshown). When both positive and negative polarities of the differentialsignal lines 145 are driven low, the LOS detector 150 determines thatthe TX 125 has stopped transmitting and the differential signal lines145 are available for the TX 130 to begin transmitting (e.g., such asaccording to eUSB2 protocols). In some examples, a limited edge rate(e.g., limited rise time and/or fall time) in a signal path of signalson the differential signal lines 145 causes a non-overlapping region inoutputs of the comparators of the LOS detector 150. The non-overlappingregion is, in some examples, a period of time between a point at which asignal present on the positive polarity of the differential signal lines145 falls below a threshold and a later point at which a signal presenton the negative polarity of the differential signal lines 145 risingabove the threshold, or vice versa. To prevent false LOS triggers by theLOS detector 150 when determining the magnitude of both positive andnegative polarities of the differential signal lines 145, in at leastsome examples the LOS detector 150 implements one or more positivefeedback circuits (not shown). The positive feedback circuits, in atleast some examples, provide positive feedback to outputs of thecomparators of the LOS detector 150 to mitigate, reduce, eliminate,and/or compensate for the non-overlapping region in the outputs of thecomparators of the LOS detector 150. The outputs of the comparators,with the added positive feedback, are processed by one or more logiccircuits (not shown) to generate a final LOS output signal of the LOSdetector 150. In some examples, the one or more logic circuits includean AND logic circuit, an inverting AND (NAND logic circuit), a buffer(e.g., an inverter logic circuit), or any other circuit suitable ofimplementing a logical function. In at least some examples, the positivefeedback of the positive feedback circuits mitigates false LOStriggering by the LOS detector 150 and eliminates a need to include afilter in an output signal path of the LOS detector 150 for preventing anon-overlapping region in an output of comparators of the LOS detector150 causing a false LOS detection trigger. In at least some examples,one or more filters are implemented in the LOS detector 150 other thanin the output signal path of the LOS detector 150.

Turning now to FIG. 2, a schematic diagram of an illustrative circuit200 is shown. In at least some examples, the circuit 200 is suitable forimplementation as a LOS detector. For example, at least someimplementations of the circuit 200 are suitable for implementation asthe LOS detector 150 of the system 100 of FIG. 1. The circuit 200includes, in some examples, a comparator 202, a comparator 204, afeedback circuit 206, a feedback circuit 208, an inverter 210, aninverter 212, a logic circuit 214, an inverter 216, a logic circuit 218,a resistor 220, and a capacitor 222. The feedback circuit 206 is, insome examples, a positive feedback circuit that includes a switch 224,an inverter 226, an inverter 228, and a switch 230. The feedback circuit208 is, in some examples, a positive feedback circuit that includes aswitch 232, an inverter 234, an inverter 236, and a switch 238.

While only the feedback circuit 206 is shown as being coupled between anode 248 and a node 250 in the circuit 200, in various examples anynumber of feedback circuits substantially similar in architecture andoperation to the feedback circuit 206 are coupled between the node 248and the node 250. Adding additional feedback stages between the node 248and the node 250, in at least some examples, provides programmability toadapt to variations in differential input signal edge rate and channelloss profiles. In at least some examples, each feedback circuit includedin the circuit 200 is isolated from other feedback circuits byinverters, such as illustrated by the inverter 210 and the inverter 212isolating the feedback circuit 206 from the feedback circuit 208. In yetother examples, each programmable stage of the circuit 200 (where aprogrammable stage includes one or more feedback circuits that areprogrammable to provide positive feedback according to a control signal(SW_EN) while another programmable stage does not provide positivefeedback for the same value of SW_EN) is isolated from other feedbackcircuits by inverters, such as illustrated by the inverter 210 and theinverter 212 isolating the feedback circuit 206 from the feedbackcircuit 208.

In at least some examples, when an even number of inverters are inseries between the node 248 and the first input terminal of the logiccircuit 214 (and similarly between the node 250 and the second inputterminal of the logic circuit 214, the logic circuit 214 is implementedto perform a logical OR operation (e.g., OR when the inverter 216 isincluded in the circuit 200 or NOR when the inverter 216 is not includedin the circuit 200). In at least some examples, when an odd number ofinverters are in series between the node 248 and the first inputterminal of the logic circuit 214 (and similarly between the node 250and the second input terminal of the logic circuit 214, the logiccircuit 214 is implemented to perform a logical AND operation (e.g., ANDwhen the inverter 216 is not included in the circuit 200 or NAND whenthe inverter 216 is included in the circuit 200). Further, in at leastsome examples, the feedback circuit 208, inverter 210, and inverter 212are omitted from the circuit 200 such that substantially all positivefeedback provided in the circuit 200 is provided by the feedback circuit206 and the logic circuit 214 is implemented to perform a logical ORoperation (e.g., OR when the inverter 216 is included in the circuit 200or NOR when the inverter 216 is not included in the circuit 200). In yetother examples, the feedback circuit 208 is omitted from the circuit 200such that substantially all positive feedback provided in the circuit200 is provided by the feedback circuit 206 and the logic circuit 214 isimplemented to perform a logical AND operation (e.g., AND when theinverter 216 is not included in the circuit 200 or NAND when theinverter 216 is included in the circuit 200). In at least some examples,in which further or additional feedback circuits are included in thecircuit 200, one or more additional logic circuits (not shown) areincluded in the circuit 200 to control which of the feedback circuitsare active at a given time, providing programmability to a multi-stagepositive feedback system. As one example, the additional logic circuitsperform an AND logic operation between a signal present at a node 266,as is discussed in greater detail below, and an enabling signal for arespective feedback circuit to enable or disable that respectivefeedback circuit.

In at least some implementations of the circuit 200, the comparator 202has a first input coupled to a node 240, a second input coupled to anode 242, and an output coupled to the node 248. The comparator 204 hasa first input coupled to the node 242, a second input coupled to thenode 240, and an output coupled to the node 250. In at least someexamples, the node 240 is configured to receive a positive polarity of adifferential input signal and the node 242 is configured to receive anegative polarity of the differential input signal. The feedback circuit206 is coupled between the node 248 and the node 250. The inverter 210is coupled between the node 248 and the node 256. The inverter 212 iscoupled between the node 250 and the node 258. The feedback circuit 208is coupled between the node 256 and the node 258. The logic circuit 214has a first input coupled to the node 256, a second input coupled to thenode 258, and an output. The inverter 216 is coupled between the outputof the logic circuit 214 and a node 264. The logic circuit 218 has afirst input coupled to the node 248, a second input coupled to the node250, and an output coupled through the resistor 220 to the node 266. Thecapacitor 222 is coupled between the node 266 and a ground node 268. Inat least some examples of the feedback circuit 206, the switch 224 iscoupled between the node 248 and a node 252, the switch 230 is coupledbetween the node 250 and the node 254, the inverter 226 has an inputcoupled to the node 254 and an output coupled to the node 252, and theinverter 228 has an input coupled to the node 252 and an output coupledto the node 254. In at least some examples of the feedback circuit 208,the switch 232 is coupled between the node 256 and a node 260, theswitch 238 is coupled between the node 258 and the node 262, theinverter 234 has an input coupled to the node 262 and an output coupledto the node 260, and the inverter 236 has an input coupled to the node260 and an output coupled to the node 262. Each of the switch 224, theswitch 230, the switch 232, and the switch 238 have a control terminalcoupled to (or are otherwise configured to be controlled by) the node266. For example, in at least some implementations the switch 224, theswitch 230, the switch 232, and the switch 238 are transistor deviceseach having a gate terminal coupled to the node 266 or each controlledat least partially according to the signal present at the node 266(e.g., such as directly controlled by one or more logic circuits (notshown) that perform one or more operations utilizing the signal presentat the node 266 as an input.

In an example of operation of the circuit 200, the comparator 202 andcomparator 204 are each coupled to differential signal lines todetermine a magnitude of a signal present on the differential signallines. For example, the comparator 202 is configured to receive a signal(LOS_INP) from a positive polarity of a differential input signal at apositive input terminal of the comparator and a signal (LOS_INM) from anegative polarity of the differential input signal at a negative inputterminal of the comparator 202. Similarly, the comparator 204 isconfigured to receive LOS_INM at a positive input terminal of thecomparator 204 and receive LOS_INP at a negative input terminal of thecomparator 204. Based on the determined magnitude, the comparator 202generates an output CMP_OUT1 and the comparator 204 generates an outputCMP_OUT2. For example, when the comparator 202 determines that a valueof LOS_INP-LOS_INM has fallen below a value of a reference threshold(e.g., an internal reference threshold of the comparator 202) , thecomparator 202 outputs CMP_OUT1 having a de-asserted, or logical low,value. Conversely, when the comparator 202 determines that a value ofLOS_INP-LOS_INM is equal to or greater than the value of the referencethreshold of the comparator 202, the comparator 202 outputs CMP_OUT1having an asserted, or logical high, value. Similarly, when thecomparator 204 determines that a value of LOS_INM-LOS_INP has fallenbelow a value of a reference threshold (e.g., an internal referencethreshold of the comparator 204), the comparator 204 outputs CMP_OUT2having a de-asserted, or logical low, value. Conversely, when thecomparator 204 determines that a value of LOS_INP-LOS_INM is equal to orgreater than the value of the reference threshold of the comparator 204,the comparator 204 outputs CMP_OUT2 having an asserted, or logical high,value.

In at least some examples, both CMP_OUT1 and CMP_OUT2 are de-assertedwhen an LOS event has occurred. However, in at least some examples,during a normal data bit transition of a differential signal transmittedvia the differential signal lines to which the comparator 202 and thecomparator 204 are coupled, CMP_OUT1 and CMP OUT2 are both de-assertedwhen an LOS event has not occurred. This creates a non-overlappingregion in CMP_OUT1 and CMP_OUT2. This non-overlapping region, in someexamples, causes a false trigger in a LOS detection output signal(LOS_OUT), leading to the inclusion of a glitch, or erroneous output, inLOS_OUT corresponding in duration to the non-overlapping region ofCMP_OUT1 and CMP_OUT2. To mitigate this glitch, as discussed above, someLOS detector implementations include a filter that filters LOS_OUT,creating a delay in output (such as, often, about 2 UI) of LOS_OUT suchthat a filtering approach is sometimes incompatible with a fastdetection circuit specification or requirement. Therefore, the circuit200 does not include a filter in an output signal path of the circuit200 to mitigate inclusion of a glitch in LOS_OUT resulting from thenon-overlapping region of CMP_OUT1 and CMP_OUT2, but instead implementsthe feedback circuit 206 and the feedback circuit 208 to mitigate theexistence of the non-overlapping region of CMP_OUT1 and CMP_OUT2 suchthat the non-overlapping region of CMP_OUT1 and CMP_OUT2 does not existto cause a glitch in LOS_OUT.

The logic circuit 218 is, in some examples, a circuit capable of and/orsuitable for performing a logical OR operation. When either CMP_OUT1 orCMP_OUT2, or both CMP_OUT1 and CMP_OUT2, are asserted, the logic circuit218 outputs a signal that also is asserted. The resistor 220 and thecapacitor 222 form a resistor-capacitor (RC) filter such that a value ofSW_EN present at the node 266 increases with time according to an RCconstant of the resistor 220 and the capacitor 222. In at least someexamples, the circuit 200 further includes supplementary circuitry (notshown) that charges the capacitor 222 at startup of the circuit 200 toinitialize the capacitor 222 and prepare it for operation in generatingSW_EN as described herein. SW_EN controls activation and deactivation ofthe feedback circuit 206 and the feedback circuit 208. For example, whena value of SW_EN rises above a switching threshold (e.g., is sufficientto cause the switch 224, the switch 230, the switch 232, and/or theswitch 238 to begin conducting), the feedback circuit 206 and thefeedback circuit 208 are enabled and provide feedback. When the value ofSW_EN is less than the switching threshold, the feedback circuit 206 andthe feedback circuit 208 are disabled and do not provide feedback. Inthis way, when both CMP_OUT1 and CMP_OUT2 are de-asserted, node 266rapidly discharges to turn off the feedback circuit 206 and the feedbackcircuit 208 and enable accurate LOS detection by the circuit 200.However, by implementing the feedback of the feedback circuit 206 andthe feedback circuit 208, based on control exerted by SW_EN, thenon-overlapping region is mitigated such that CMP_OUT1 and CMP_OUT2 havea non-zero value overlap until LOS occurs. For example, a positivefeedback circuit such as the feedback circuit 206 and/or the feedbackcircuit 208 has a high regenerative gain, thereby causing the feedbackcircuit to amplify small differences between signal paths. In thecircuit 200, during normal signal transitions of the differential inputsignal, when the comparator 202 output rapidly drops and the comparator204 output stays at a ground level, the positive feedback begins andslows a falling edge rate of the signal present at the node 248decreases in value while gradually increasing in value the signalpresent at the node 250. This maintains the signal present at the node248 as an analog inversion of the signal present at the node 250,mitigating, reducing, and/or eliminating a non-over-lapping region inthe signal present at the node 248 and the signal present at the node250.

For example, when SW_EN causes the switch 224 and the switch 230 toenter conductive states, coupling the node 248 to the node 252 and thenode 250 to the node 254, respectively, the feedback of the feedbackcircuit 206 is enabled. When the feedback of the feedback circuit 206 isenabled, the inverter 226 inverts a signal present at the node 254 toprovide positive feedback at the node 252 and the inverter 228 inverts asignal present at the node 252 to provide positive feedback at the node254. The feedback is referred to as positive feedback because itreinforces a value of a signal already present at the node receiving thepositive feedback.

The signals present at the node 248 and the node 250 are inverted invalue by the inverter 210 and the inverter 212, respectively, to providesignals at the node 256 and the node 258. The feedback circuit 208provides further positive feedback at the node 256 and the node 258 insubstantially the same manner as the feedback circuit 206 at the node248 and the node 250, and detailed description of operation is notrepeated herein for the feedback circuit 208, but instead reference ismade to the description of like components of the feedback circuit 206.The logic circuit 214, in some examples, performs an inverting ANDoperation on signals present at the node 256 and the node 258 togenerate an inverted version of LOS_OUT (LOS_OUTZ) which is subsequentlyinverted by the inverter 216 to form LOS_OUT that is provided at thenode 264. In at least some examples, such as when the circuit 200 isconfigured to couple at the node 264 to a device or component having asmall capacitive load, the logic circuit 214 performs an AND operationon signals present at the node 256 and the node 258 and the inverter 216is omitted such that an output of the logic circuit 214 is provided atthe node 264.

In at least some examples, the above feedback-based scheme and circuitfor determining LOS and generating LOS_OUT improves over alternativecircuit arrangements and processes in circuit size and speed. Forexample, alternatives that incorporate a RC filter for filtering LOS_OUTsuffer from increased circuit size, cost, power consumption, and timefrom a LOS event occurring to generation of LOS_OUT indicating that theLOS event has occurred. Similarly, approaches utilizing a clock or PLLsuffer from increased circuit size, cost, power consumption. At leastsome of these negative aspects of alternative approaches are mitigatedand/or improved upon by the teachings of the present disclosure,including at least the use of switchable positive feedback provided bythe feedback circuit 206 and/or the feedback circuit 208, such that thecircuit 200 consumes less physical space and/or less power, costs lessto implement, and/or determines LOS_OUT more rapidly than at least someof the alternative approaches described above.

Turning now to FIG. 3, a diagram 300 of illustrative signal waveforms isshown. In at least some examples, the diagram 300 is illustrative of atleast some signals present in the circuit 200 of FIG. 2 and/or thesystem 100 of FIG. 1. For example, the signals LOS_INP, LOS_INM,CMP_OUT1, CMP_OUT2, and LOS_OUT, according to one implementation of thecircuit 200, are illustrated in the diagram 300. Additionally, thediagram 300 includes CMP_OUT1* and CMP_OUT2* which illustrate CMP_OUT1and CMP_OUT2, respectively, in the absence of the teachings of thepresent disclosure (e.g., in the absence of circuitry and/or processingthat mitigates the non-overlapping region shown for CMP_OUT1* andCMP_OUT2* between points t1 and t2).

As shown by diagram 300, and discussed above with respect to the circuit200, CMP_OUT1* is asserted when LOS_INP-LOS_INM has a value greater thana threshold designated as x1. Similarly, CMP_OUT2* is de-asserted whenLOS_INM-LOS_INP has a value less than x1. In at least some examples, x1is approximately equal to VCM+VTH/2 where VCM is a common mode voltageof LOS_INP and LOS_INM and VTH is the internal reference threshold ofthe comparator 202 and comparator 204, discussed above with respect toFIG. 2. This creates a non-overlapping region for CMP_OUT1* andCMP_OUT2* between t1 and t2. This leads to a false LOS detection,designated in the diagram 300 by reference 305, being present inLOS_OUT, which detrimentally affects operations of one or more systems,circuits, or components that receive LOS_OUT. However, as shown byCMP_OUT1 and CMP_OUT2, under the teachings of the present disclosure thenon-overlapping region between t1 and t2 is mitigated such that thefalse LOS detection 305 will not be present in LOS_OUT. For example, att1 when LOS_INP-LOS_INM falls below x1, CMP_OUT1 begins to decrease invalue until CMP_OUT1 is de-asserted at time t2. Similarly, at t1 whenLOS_INM-LOS_INP rises above a second threshold designated as x2,CMP_OUT2 begins to increase in value until CMP_OUT2 is asserted at timet2. In at least some examples, x2 is approximately equal to VCM-VTH/2.In this way, no non-overlapping period exists between t1 and t2 when atransition occurs in LOS_INP and LOS_INM. At time t3, LOS_INM-LOS_INP(or LOS_INP-LOS_INM, depending on a pattern polarity of LOS_INP andLOS_INM) falls below x1 such that CMP_OUT2 becomes de-asserted, at whichtime SW_EN also becomes de-asserted. Both CMP_OUT1 and CMP_OUT2 beingde-asserted indicates that a LOS event has occurred and triggers LOS_OUTto become asserted at time t4.

Turning now to FIG. 4, a flowchart of an illustrative method 400 isshown. In at least some examples, the method 400 is a method of signaldetection, such as LOS detection, and corresponds to one or morehardware components, circuits, devices, or systems disclosed here. Forexample, at least some portions of the system 100 and/or circuit 200implement or perform one or more operations of the method 400.

At operation 405, magnitudes of positive and negative components of adifferential input signal are determined. The magnitudes are determined,in some examples, by differential comparators. At operation 410, aswitch control signal is generated. The switch control signal isgenerated, in some examples, by a time-dependent circuit, such as an RCtimer or RC filter circuit in which a value of the switch control signalincreases or decreases with time according to a time constant of thetime-dependent circuit. The switch control signal, in at least someexamples, controls enablement or disablement of one or more feedbackcircuits for providing positive feedback in a circuit including thedifferential comparators. The switch control signal, in some examples,increases in value when at least one determined magnitude of thepositive or negative components of a differential input signal isnon-zero. When neither determined magnitude is non-zero, the method 400proceeds to operation 415. When at least one determined magnitude isnon-zero and the switch control signal has increased in value above aswitching threshold, the method 400 proceeds to operation 420. Atoperation 415, a LOS output is generated according to the determinedmagnitudes. The LOS output generated at operation 415, in some examples,indicates that a LOS event has occurred. In some examples, outputsignals of the differential comparators are processed by one or morelogic circuits to generate the LOS output at operation 415. At operation420, positive feedback is enabled. The positive feedback is enabled, insome examples, based on a value of the switch control signal. Thepositive feedback prevents and/or mitigates the existence of anon-overlapping region in the output signals of the differentialcomparators when a LOS event has not occurred (e.g., such as duringnormal transitioning of the output signals of the differentialcomparators during a bit transition of the differential input signal).At operation 425, the LOS output is generated according to thedetermined magnitudes and the positive feedback. The LOS outputgenerated at operation 425, in some examples, indicates that a LOS eventhas not occurred. Generating the LOS output according to the determinedmagnitudes and the positive feedback, in at least some examples,prevents formation of a glitch or erroneous LOS trigger in the LOSoutput resulting from a non-overlapping region in the output signals ofthe differential comparators.

While the operations of the method 400 have been discussed and labeledwith numerical reference, in various examples the method 400 includesadditional operations that are not recited herein, in some examples anyone or more of the operations recited herein include one or moresub-operations (e.g., such as intermediary comparisons, logicaloperations, output selections such as via a multiplexer, etc.), in someexamples any one or more of the operations recited herein is omitted,and/or in some examples any one or more of the operations recited hereinis performed in an order other than that presented herein (e.g., in areverse order, substantially simultaneously, overlapping, etc.), all ofwhich is intended to fall within the scope of the present disclosure.

In the foregoing discussion, the terms “including” and “comprising” areused in an open-ended fashion, and thus should be interpreted to mean“including, but not limited to. . . .” The term “couple” is usedthroughout the specification. The term may cover connections,communications, or signal paths that enable a functional relationshipconsistent with the description of the present disclosure. For example,if device A generates a signal to control device B to perform an action,in a first example device A is coupled to device B, or in a secondexample device A is coupled to device B through intervening component Cif intervening component C does not substantially alter the functionalrelationship between device A and device B such that device B iscontrolled by device A via the control signal generated by device A. Adevice that is “configured to” perform a task or function may beconfigured (e.g., programmed and/or hardwired) at a time ofmanufacturing by a manufacturer to perform the function and/or may beconfigurable (or re-configurable) by a user after manufacturing toperform the function and/or other additional or alternative functions.The configuring may be through firmware and/or software programming ofthe device, through a construction and/or layout of hardware componentsand interconnections of the device, or a combination thereof.Furthermore, a circuit or device that is said to include certaincomponents may instead be configured to couple to those components toform the described circuitry or device. For example, a structuredescribed as including one or more semiconductor elements (such astransistors), one or more passive elements (such as resistors,capacitors, and/or inductors), and/or one or more sources (such asvoltage and/or current sources) may instead include only thesemiconductor elements within a single physical device (e.g., asemiconductor die and/or integrated circuit (IC) package) and may beconfigured to couple to at least some of the passive elements and/or thesources to form the described structure either at a time of manufactureor after a time of manufacture, for example, by an end-user and/or athird-party.

While certain components are described herein as being of a particularprocess technology (e.g., FET, MOSFET, n-type, p-type, etc.), thesecomponents may be exchanged for components of other process technologies(e.g., replace FET and/or MOSFET with bi-polar junction transistor(BJT), replace n-type with p-type or vice versa, etc.) and reconfiguringcircuits including the replaced components to provide desiredfunctionality at least partially similar to functionality availableprior to the component replacement. Components illustrated as resistors,unless otherwise stated, are generally representative of any one or moreelements coupled in series and/or parallel to provide an amount ofimpedance represented by the illustrated resistor. Additionally, uses ofthe phrase “ground voltage potential” in the foregoing discussion areintended to include a chassis ground, an Earth ground, a floatingground, a virtual ground, a digital ground, a common ground, and/or anyother form of ground connection applicable to, or suitable for, theteachings of the present disclosure. Unless otherwise stated, “about”,“approximately”, or “substantially” preceding a value means +/−10percent of the stated value.

The above discussion is meant to be illustrative of the principles andvarious examples of the present disclosure. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the presentdisclosure be interpreted to embrace all such variations andmodifications.

What is claimed is:
 1. A LOS (loss of signal) detector circuitcomprising: a first differential comparator having a first input, asecond input, and an output; a second differential comparator having afirst input coupled to the second input of the first differentialcomparator, a second input coupled to the first input of the firstdifferential comparator, and an output; a first switched latch circuithaving a first input coupled to the output of the first differentialcomparator, a second input coupled to the output of the seconddifferential comparator and a control input; a first inverter having aninput coupled to the output of the first differential comparator and anoutput; a second inverter having an input coupled to the output of thesecond differential comparator and an output; and a first logic circuithaving a first input coupled to the output of the first inverter, asecond input coupled to the output of the second inverter and an output.2. The LOS detector circuit of claim 1, further comprising a secondswitched latch circuit coupled to the output of the first inverter andto the output of the second inverter.
 3. The LOS detector circuit ofclaim 1, wherein the first logic circuit comprises an inverting AND(NAND) logic circuit.
 4. The LOS detector circuit of claim 3, furthercomprising a third inverter having an input coupled to the output of thefirst logic circuit and an output.
 5. The LOS detector circuit of claim1, further comprising: a second logic circuit having a first inputcoupled to the output of the first differential comparator, a secondinput coupled to the output of the second differential comparator and anoutput; a resistor having a first terminal coupled to the output of thesecond logic circuit and a second terminal; and a capacitor having afirst terminal coupled the second terminal of the resistor and a secondterminal coupled to ground.
 6. The LOS detector circuit of claim 5,wherein a switch control signal is generated at the first terminal ofthe capacitor and coupled to the control input of the first switchedlatch circuit, and wherein the switch control signal controls enablementand disablement of the first switched latch circuit.
 7. The LOS detectorcircuit of claim 1, wherein the first switched latch circuit comprises:a first switch having a first terminal coupled to the output of thefirst differential comparator, a second terminal, and a third terminalcoupled to the control input; a second switch having a first terminalcoupled to the output of the second differential comparator, a secondterminal and a third terminal coupled to the control input; a fourthinverter having an input coupled to the second terminal of the firstswitch and an output coupled to the second terminal of the secondswitch; and a fifth inverter having an input coupled to the secondterminal of the second switch and an output coupled to the secondterminal of the first switch.
 8. A system comprising: an eUSB2 (embeddeduniversal serial bus 2) device having bi-directional ports operating inboth ingress and egress communication; a processor having a first pairof bi-directional ports adaptively coupled to the bi-directional portsof the eUSB2 device, and a second pair of bi-direction ports operatingin both ingress and egress communication; an USB (universal serial bus)device having bi-direction ports operating in both ingress and egresscommunication; an eUSB2 repeater comprising: a receiver having a firstpair of bi-directional ports for receiving differential data from theprocessor or from the USB device, and a pair of differential signalterminals; a transmitter having a second pair of bi-directional portsfor transmitting differential data to the processor or to the USB devicewherein the transmitter is coupled to the pair of differential signalterminals; and a LOS (loss of signal) detection circuit coupled to thereceiver and the transmitter wherein the LOS circuit determines when thetransmitter has stopped transmitting differential data to the receiver.9. The system of claim 8 wherein the LOS detection circuit furthercomprises: a first differential comparator having a first input, asecond input, and an output; a second differential comparator having afirst input coupled to the second input of the first differentialcomparator, a second input coupled to the first input of the firstdifferential comparator, and an output; a first switched latch circuithaving a first input coupled to the output of the first differentialcomparator, a second input coupled to the output of the seconddifferential comparator and a control input; a first inverter having aninput coupled to the output of the first differential comparator and anoutput; a second inverter having an input coupled to the output of thesecond differential comparator and an output; and a first logic circuithaving a first input coupled to the output of the first inverter, asecond input coupled to the output of the second inverter and an output.10. The system of claim 9, further comprising a second switched latchcircuit coupled to the output of the first inverter and to the output ofthe second inverter.
 11. The system of claim 9, wherein the first logiccircuit comprises an inverting AND (NAND) logic circuit.
 12. The systemof claim 9, further comprising a third inverter having an input coupledto the output of the first logic circuit and an output.
 13. The systemof claim 9, further comprising: a second logic circuit having a firstinput coupled to the output of the first differential comparator, asecond input coupled to the output of the second differential comparatorand an output; a resistor having a first terminal coupled to the outputof the second logic circuit and a second terminal; and a capacitorhaving a first terminal coupled the second terminal of the resistor anda second terminal coupled to ground node.
 14. The system of claim 13,wherein a switch control signal is generated at the first terminal ofthe capacitor and coupled to the control input of the first switchedlatch circuit, and wherein the switch control signal controls enablementand disablement of the first switched latch circuit.
 15. The system ofclaim 9, wherein the first switched latch circuit comprises: a firstswitch having a first terminal coupled to the output of the firstdifferential comparator, a second terminal, and a third terminal coupledto the control input; a second switch having a first terminal coupled tothe output of the second differential comparator, a second terminal anda third terminal coupled to the control input; a fourth inverter havingan input coupled to the second terminal of the first switch and anoutput coupled to the second terminal of the second switch; and a fifthinverter having an input coupled to the second terminal of the secondswitch and an output coupled to the second terminal of the first switch.16. A system comprising: an eUSB2 (embedded universal serial bus 2)device having bi-directional ports operating in both ingress and egresscommunication; an USB (universal serial bus) device having bi-directionports operating in both ingress and egress communication; an eUSB2repeater comprising: a receiver having a first pair of bi-directionalports for receiving differential data from the eUSB2 device or from theUSB device, and a pair of differential signal terminals; a transmitterhaving a second pair of bi-directional ports for transmittingdifferential data to the eUSB2 device or to the USB device wherein thetransmitter is coupled to the pair of differential signal terminals; anda LOS (loss of signal) detection circuit coupled to the receiver and thetransmitter wherein the LOS circuit determines when the transmitter hasstopped transmitting differential data to the receiver.
 17. The systemof claim 16 wherein the LOS detection circuit further comprises: a firstdifferential comparator having a first input, a second input, and anoutput; a second differential comparator having a first input coupled tothe second input of the first differential comparator, a second inputcoupled to the first input of the first differential comparator, and anoutput; a first switched latch circuit having a first input coupled tothe output of the first differential comparator, a second input coupledto the output of the second differential comparator and a control input;a first inverter having an input coupled to the output of the firstdifferential comparator and an output; a second inverter having an inputcoupled to the output of the second differential comparator and anoutput; and a first logic circuit having a first input coupled to theoutput of the first inverter, a second input coupled to the output ofthe second inverter and an output.
 18. The system of claim 17, furthercomprising a second switched latch circuit coupled to the output of thefirst inverter and to the output of the second inverter.
 19. The systemof claim 17, wherein the first logic circuit comprises an inverting AND(NAND) logic circuit.
 20. The system of claim 17, further comprising athird inverter having an input coupled to the output of the first logiccircuit and an output.
 21. The system of claim 17, further comprising: asecond logic circuit having a first input coupled to the output of thefirst differential comparator, a second input coupled to the output ofthe second differential comparator and an output; a resistor having afirst terminal coupled to the output of the second logic circuit and asecond terminal; and a capacitor having a first terminal coupled thesecond terminal of the resistor and a second terminal coupled to groundnode.
 22. The system of claim 21, wherein a switch control signal isgenerated at the first terminal of the capacitor and coupled to thecontrol input of the first switched latch circuit, and wherein theswitch control signal controls enablement and disablement of the firstswitched latch circuit.
 23. The system of claim 17, wherein the firstswitched latch circuit comprises: a first switch having a first terminalcoupled to the output of the first differential comparator, a secondterminal, and a third terminal coupled to the control input; a secondswitch having a first terminal coupled to the output of the seconddifferential comparator, a second terminal and a third terminal coupledto the control input; a fourth inverter having an input coupled to thesecond terminal of the first switch and an output coupled to the secondterminal of the second switch; and a fifth inverter having an inputcoupled to the second terminal of the second switch and an outputcoupled to the second terminal of the first switch.
 24. A method forreducing false LOS (loss of signal) triggers comprising: determinemagnitudes of components of a differential input signal provided toinputs of first and second differential comparators; generate a LOSsignal when the magnitudes of the components of the differential signalare all below a threshold voltage; generate a switch control signal whenany of the components of the differential signal are above the thresholdvoltage; apply positive feedback to a signal across an output of thefirst differential comparator and an output of the second differentialcomparator when the switch control is generated; generate the LOS signalbased on the signal across the output of the first differentialcomparator and the output of the second differential comparator afterpositive feedback has been applied.